High-Affinity Chemotaxis to Histamine Mediated by the TlpQ Chemoreceptor of the Human Pathogen Pseudomonas aeruginosa

Histamine is a key biological signaling molecule. It acts as a neurotransmitter in the central and peripheral nervous systems and coordinates local inflammatory responses by modulating the activity of different immune cells. During inflammatory processes, including bacterial infections, neutrophils stimulate the production and release of histamine. Here, we report that the opportunistic human pathogen Pseudomonas aeruginosa exhibits chemotaxis toward histamine. This chemotactic response is mediated by the concerted action of the TlpQ, PctA, and PctC chemoreceptors, which display differing sensitivities to histamine. Low concentrations of histamine were sufficient to activate TlpQ, which binds histamine with an affinity of 639 nM. To explore this binding, we resolved the high-resolution structure of the TlpQ ligand binding domain in complex with histamine. It has an unusually large dCACHE domain and binds histamine through a highly negatively charged pocket at its membrane distal module. Chemotaxis to histamine may play a role in the virulence of P. aeruginosa by recruiting cells at the infection site and consequently modulating the expression of quorum-sensing-dependent virulence genes. TlpQ is the first bacterial histamine receptor to be described and greatly differs from human histamine receptors, indicating that eukaryotes and bacteria have pursued different strategies for histamine recognition.